In the past, the predominant cleaning method for cleaning the interior of pipes, tanks, and other containers employed the use of high pressure water systems. Such systems required workers to physically enter tanks containing hazardous residues. Because of the danger to workers, OSHA has strengthened regulations relating to confined entry (Occupational Safety and Health Standards, Part 1910, Subsection 146). These regulations now require such costly safety equipment and procedures that the market is eagerly searching for ways to adopt new cleaning systems which minimize or eliminate the need for workers to enter tanks. In addition, the large volume of water and waste material generated by these high pressure water systems must be handled and disposed of properly.
Accordingly, methods and apparatus for using solvent vapor to clean the interior surfaces of a container, such as a tank or objects suspended therein have been proposed. For example, U.S. Pat. No. 2,023,496 discloses a method whereby a liquid solvent or diluent is heated and then applied to oil-covered surfaces of a tank or vessel. The solvent acts to liquify the oily deposits so as to release the deposit from the interior surface of the tank. Similarly, U.S. Pat. No. 3,046,163 teaches a method of cleaning the interior of a tank holding oil, grease, crude petroleum products, coal tar products, resinous products, paints or plasticizers comprising the steps of first passing hot vapor of a chlorinated hydrocarbon solvent into the tank and condensing the vapor on the tank walls, thereby dissolving adhering dissolvable matter on the interior surfaces of the tank.
The efficiency and efficacy of the cleaning apparatus is dependent largely on the efficiency of the vapor forming process in the first instance, and additionally vapor concentration within the container being cleaned. However, the prior art vaporizing processes have been found to be inefficient due to the relatively inefficient mechanisms for forming the vapor such that quantities of solvent remained liquified, and hence unusable. In addition, prior methods generally produce relatively low concentrations of vapor in the air stream which is being used to clean the interior of the container.